US9097585B2ActiveUtilityA1

Spectrographic polarimeter and method of recording state of polarity

61
Individually held — no corporate assignee on recordPriority: Sep 8, 2011Filed: Sep 10, 2012Granted: Aug 4, 2015
Est. expirySep 8, 2031(~5.1 yrs left)· nominal 20-yr term from priority
Inventors:William B. Sparks
G01J 3/447G01J 3/44
61
PatentIndex Score
2
Cited by
15
References
31
Claims

Abstract

A single-shot real-time spectropolarimeter for use in astronomy and other sciences that captures and encodes some or all of the Stokes polarization parameters simultaneously using only static, robust optical components with no moving parts is described. The polarization information is encoded onto the spectrograph at each wavelength along the spatial dimension of the 2D output data array. The varying embodiments of the concept include both a two-Stokes implementation (in which any two of the three Stokes polarization parameters are measured) and a full Stokes implementation (in which all three of the Stokes polarization parameters are measured), each of which is provided in either single beam or dual beam forms.

Claims

exact text as granted — not AI-modified
What is claimed: 
     
       1. A point-and-shoot spectropolarimeter for measuring at least one polarization parameter of incident light and recording said at least one polarization parameter in a single spectropolarimetric frame, comprising
 an entrance slit along an optical path of said incident light; 
 a first birefringent wedge positioned along said optical path and having a fast axis at 45° to said slit, and a thickness gradient along said slit; 
 a polarization analyzer having an axis of transmission at a known angle relative to said slit; and 
 a collimator for collimating diverging light from said polarization analyzer; 
 a disperser for producing optical spectra by diffraction or refraction of said collimated light; 
 a focusing optic for focusing the optical spectra onto a detector array; 
 a rectangular detector array for detecting intensity of light passed by said polarization analyzer along a spatial axis and wavelength of light passed by said polarization analyzer along a spectral axis; 
 whereby the intensity of light detected by said detector array is modulated along said spatial axis as a function of said at least one polarization parameter of said incident light to create an intensity-modulated waveform imaged onto said detector array and polarization measurements can be decoded from a single frame imaged at said detector array. 
 
     
     
       2. The spectropolarimeter of  claim 1 , wherein said at least one polarization parameter of said incident light comprises a first Stokes vector Q and a second Stokes vector V of said incident light, and
 wherein the intensity of light detected by said intensity sensor is modulated on a spatial axis of said sensor as a function of said first and second Stokes vectors Q,V of said incident light. 
 
     
     
       3. The spectropolarimeter of  claim 2 , wherein said at least one polarimetry parameter of said incident light further comprises three polarimetry parameters of said incident light, and the intensity of light detected by said intensity sensor is modulated on a spatial axis of said detector array as a function of said three polarimetry parameters of said incident light. 
     
     
       4. The spectropolarimeter of  claim 1 , further comprising a second bi-refringent wedge having an optical axis oriented orthogonally to said first bi-refringent wedge. 
     
     
       5. The spectropolarimeter of  claim 4 , wherein said second bi-refringent wedge is attached to said first bi-refringent wedge. 
     
     
       6. The spectropolarimeter of  claim 2 , further comprising:
 a quarter-wave plate along said optical path with fast axis along a direction of the slit before said first birefringent wedge, said first polarimetry parameter of said incident light being a measure of linear polarization in a first plane perpendicular to a direction of wave propagation and said second polarimetry parameter of said incident light being a measure of linear polarization in a second plane perpendicular to the direction of wave propagation, said second plane being at 45 degrees to said first plane. 
 
     
     
       7. The spectropolarimeter of  claim 3 , further comprising
 a second birefringent wedge along said optical path, either parallel or anti-parallel to said first birefringent wedge, and having twice the birefringence of said first birefringent wedge and having a fast axis at 45° to said first birefringent wedge, said first polarimetry parameter of said incident light being a measure of linear polarization in a first plane perpendicular to a direction of wave propagation, said second polarimetry parameter of said incident light being a measure of linear polarization in a second plane perpendicular to a direction of wave propagation, and said second plane being 45 degrees to said first plane, and said third polarimetry parameter of said incident light being a measure of the circular polarization of said incident light. 
 
     
     
       8. The spectropolarimeter of  claim 7 , further comprising a third bi-refringent wedge having an optical axis oriented orthogonally to said first bi-refringent wedge. 
     
     
       9. The spectropolarimeter of  claim 8 , wherein said second bi-refringent wedge is attached to said first bi-refringent wedge. 
     
     
       10. The spectropolarimeter of  claim 8 , further comprising a fourth bi-refringent wedge having an optical axis oriented orthogonally to said second bi-refringent wedge. 
     
     
       11. The spectropolarimeter of  claim 10 , wherein said fourth bi-refringent wedge is attached to said second bi-refringent wedge. 
     
     
       12. A long slit point-and-shoot spectrometer for recording at least one polarization parameter of light in a single recorded spectropolarimetric frame, comprising:
 a spectrographic optical platform including,
 a slit, 
 a collimator, 
 a dispersing element, 
 a focusing optic, 
 a two-dimensional detector array having a length and width dimension, the width corresponding to a spectral axis oriented perpendicular to the slit for sensing intensity of incident light at each wavelength along said slit, and said length comprising a spatial axis, the collimator and focusing optic being calibrated to dispersing light from said slit over a width of said detector array for faster accumulation of photons; 
 
 a first bi-refringent wedge positioned along the optical axis before the collimator; and 
 a polarizing analyzer positioned between said wedge and collimator; 
 said first bi-refringent wedge and polarizing analyzer creating a gradient of retardance such that the intensity of light detected along the spectral axis of the detector array is modulated as a function of at least one polarization parameter to create an intensity-modulated waveform imaged onto said detector array, whereby polarization measurements can be decoded from a single frame imaged at said detector array. 
 
     
     
       13. The long-slit spectrometer of  claim 12 , further comprising an achromatic quarter wave plate before the wedge and having a fast axis aligned along the slit. 
     
     
       14. The long-slit spectrometer of  claim 12 , wherein said polarizing analyzer is a polarizing filter. 
     
     
       15. The long-slit spectrometer of  claim 12 , wherein said polarizing analyzer is a beam-splitting polarizing prism. 
     
     
       16. The long-slit spectrometer of  claim 12 , wherein said at least one polarization parameter is encoded along the spatial axis of the detector array at each wavelength along the spectral axis. 
     
     
       17. The long-slit spectrometer of  claim 12 , wherein said first birefringent wedge has a fast axis and a slow axis, and an index of refraction along said fast axis is smaller than an index of refraction along said slow axis. 
     
     
       18. The long-slit spectrometer of  claim 12 , wherein light from a light source is spread along the spatial axis of the detector array. 
     
     
       19. The long-slit spectropolarimeter of  claim 12 , further comprising a second bi-refringent wedge having an optical axis oriented orthogonally to said first bi-refringent wedge. 
     
     
       20. The long-slit spectropolarimeter of  claim 19 , wherein said second bi-refringent wedge is attached to said first bi-refringent wedge. 
     
     
       21. The long-slit spectropolarimeter of  claim 12 , further comprising a second birefringent wedge having twice the birefringence of said first birefringent wedge and having a fast axis at 45° to said first birefringent wedge. 
     
     
       22. The long-slit spectropolarimeter of  claim 21 , further comprising a third bi-refringent wedge having an optical axis oriented orthogonally to said first bi-refringent wedge. 
     
     
       23. The long-slit spectropolarimeter of  claim 22 , wherein said third bi-refringent wedge is attached to said first bi-refringent wedge. 
     
     
       24. The long-slit spectropolarimeter of  claim 23 , further comprising a fourth bi-refringent wedge having an optical axis oriented orthogonally to said second bi-refringent wedge. 
     
     
       25. The long-slit spectropolarimeter of  claim 24 , wherein said fourth bi-refringent wedge is attached to said second bi-refringent wedge. 
     
     
       26. The long-slit spectrometer of  claim 12 , wherein said first birefringent wedge comprises a fast axis rotated 45° relative to said slit and a wedge thickness gradient along the slit. 
     
     
       27. The long-slit spectrometer of  claim 12 , wherein the intensity of light detected by said detector array is modulated along said spatial axis as a function of a first Stokes polarization parameter U and a second Stokes polarization parameter V of said light. 
     
     
       28. The long-slit spectrometer of  claim 12 , wherein the intensity of light detected by said detector array is modulated along said spatial axis as a function of a first Stokes polarization parameter V and a second Stokes polarization parameter Q of said light. 
     
     
       29. The long-slit spectrometer of  claim 13 , wherein the intensity of light detected by said detector array is modulated along said spatial axis as a function of a first Stokes polarization parameter Q and a second Stokes polarization parameter U of said light. 
     
     
       30. The long-slit spectrometer of  claim 27 , wherein the intensity of light detected by said detector array is modulated along said spatial axis as a function of said first and second Stokes polarization parameters U, V and a third Stokes polarization parameter Q of said light. 
     
     
       31. The long-slit spectrometer of  claim 28 , further comprising a second, parallel slit for two beam analysis.

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